The function of the Nef protein encoded by HIV and simian immunodeficiency virus (SIV) is still unknown. Several reports propose that it is involved in viral latency due to a negative effect on viral transcription. Frequent inactivating mutations in the gene during virus isolation suggest that the gene is not tolerated well by tissue culture cells. In order to investigate the function of this gene we have generated several reagents. Expression of nef in the heterologous baculovirus expression heterologous system allows us to assess the serological status of animals infected with SIV/Mne. The protein is also purified by preparative gel electrophoresis and used to make poly- and monoclonal antibodies to replace a low titer rabbit antiserum that was made against a synthetic peptide. Furthermore, a mutant of the protein which is no longer myristylated is produced in large amounts for X-ray crystallography analysis. Nef expression constructs producing the gene product at constitutive high levels or under the control of a heat-inducible promoter have been generated to analyze the role of the Nef protein in infected and uninfected cells.